Vitro Maturation and Fertilization of Cryopreserved Germinal Vesicle Stage Oocytes in NMRI Mice, Using Ethylene Glycol and DMSO

Cryopreservation of oocytes is an essential part of reproductive biotechnology. The objective of the present study was to investigate the effects of exposure to combination of cryoprotectants and vitrification on immature mouse oocytes with or without cumulus cells. This was an experimental study conducted at Yasouj University of Medical Sciences in 2010. Immature oocytes with and without cumulus cells were isolated from ovaries of mice 4-6 weeks of age. They were vitrified in conventional straw using ethylene glycol (EG), dimethyl sulfoxide (DMSO) and sucrose as vitrification solution or exposed to vitrification solution without subjected to liquid nitrogen. After warming, oocytes were assessed for nuclear maturation and fertilization. The collected data were analyzed with one-way ANOVA and Tukey test. Survival and fertilization rates in vitrified oocytes with cumulus cells were significantly lower than the control group (p<0.05). Maturation rates in exposure groups were significantly lower than the vitrified and control groups (p<0.05). The fertilization rate increased significantly in all experiment and control groups with cumulus cells in comparison with denuded oocytes (p<0.05). Germinal vesicle stage oocytes in the presence or absence of cumulus cells can be vitrified successfully. Exposure to cryoprotectants can decrease the developmental competence of GV oocytes. Presence of cumulus cells can increase the fertilization rate in IVF procedure.